Combination battery charger/controller

ABSTRACT

A battery powered device such as an electric vehicle includes a high power loads such as a drive motor ( 50 ), and on-board charging and discharging systems ( 20 ) which share significant components such as a pulsing subsystem ( 40 ). In particularly preferred embodiments the battery ( 10 ) and regenerative braking system ( 90 ), where applicable, are selected to operate efficiently with the charging and discharging systems ( 20 ).

This application is a 371 of PCT/US98/06049, filed Mar. 26, 1998, andclaims benefit of Provisional application 60/041,838, filed Apr. 9,1997.

FIELD OF THE INVENTION

The field of the invention is battery powered devices, including batterypowered vehicles.

BACKGROUND OF THE INVENTION

Considerable resources have been invested over the last several years inthe development of battery powered devices. For many such devices,especially small consumer items such as portable electric shavers andtoothbrushes, in which the power storage and delivery requirements arenot terribly demanding, the known technologies are quite adequate. Forother devices, including portable power tools and computers, golf cartsand fork lifts, the demands are such that presently availabletechnologies are relatively satisfactory, but inconvenient. For stillother devices such as all-electric automobiles, the demands are suchthat implementation of commercially acceptable embodiments has beensignificantly impeded by excessively long charging duration, and limitedbattery capacity. Thus, there is still a need to improve power storageand delivery in battery powered devices.

There are four systems of especial importance to the overall efficiencyof battery powered devices, namely the battery or battery pack, thebattery charging system, the battery discharging system and the load.Previously, these systems were almost always developed and implementedindependently, resulting in additional inefficiencies even if theunderlying systems were themselves relatively efficient. Thus, there isa continuing need to integrate two or more of these systems in ways thatimprove the overall efficiency.

Batteries

Batteries can generally be divided into two types, those in which theelectrolyte is maintained largely in a liquid phase, as exemplified bycommon lead-acid automobile batteries, and those in which theelectrolyte is maintained largely in a solid or semi-solid phase, asexemplified by Nickel-Cadmium (NiCad) batteries. Within each type ofbattery, there are numerous possible electrolytes and electrodematerials available.

Both liquid electrolyte and solid electrolyte batteries suffer fromsignificant drawbacks. Liquid electrolyte batteries tend to leak, and toexperience electrolysis involving gas formation at boundaries of theelectrodes. These phenomena increase the apparent impedance of thebattery and cause current related heating that may result in failure ofinternal structures. Extreme cases may result in explosion. Even withoutdamage or danger of explosion, the gasses may require venting and aregenerally hazardous. Electrolysis may also cause loss of electrolytewhich is deleterious to the battery chemistry, causing reduced batterylife and increased maintenance costs.

Solid and semi-solid electrolyte batteries are more resistant toleaking, but are still prone to electrolyte degradation. Moreover, suchbatteries generally have significantly reduced power density andrelatively limited number of recharge cycles.

The problems discussed above with respect to different types ofbatteries can be exacerbated through the use of known chargingtechnologies. For example, both lead-acid and Nickel Metal Hydridebatteries can become explosive during rapid charging, especially wherethe charger does not protect against overcharging.

Battery Chargers

Battery chargers generally fall into two categories—(1) direct current(D.C.) chargers and (2) pulsed current chargers. Direct current chargerstypically utilize either a constant voltage mode in which the voltage isfixed and the current varies, or a constant current mode in which thecurrent is fixed and the voltage varies. D.C. chargers give rise toseveral problems, many of which can be reduced or eliminated by limitingthe maximum charging current to a low-value, and thereby extending thecharge cycle up to several hours. A typical low-value charging currentwould be one-tenth battery capacity, i.e., where the charging currentfalls at the battery's nominal amp-hour capacity divided by 10 hours.Thus, a ten amp-hour battery charging at a rate of 1 amp would employ alow-value charging current. Such chargers, known as trickle chargers,are advantageous in that they obviate the need for complex controlschemes, and minimize the danger of reaching an overcharge condition.This is especially true in the constant voltage mode since current willreduce even further as battery voltage approaches the voltage of thecharging source. The main drawback of trickle chargers is theinconvenience of being unable to use the battery for the 8 to 18 hoursthat are required to recharge the battery, or alternatively, the expenseof procuring additional battery packs to act as replacements during therecharge cycle. These disadvantages are especially relevant with respectto electric vehicles where the batteries cannot readily be swapped inand out of the vehicle.

In pulsed battery chargers, the charging current is turned on and offperiodically, thus allowing gases and separated ions sufficient time torecombine in the electrolyte solution. A further improvement involvesutilizing the period of recombination to apply short discharge pulses tothe battery to “clean-up” the newly plated material, thereby eliminatingcontaminants and nodules in the plated matrix. This technique wasoriginally developed and patented by G. W. Jernstedt (assigned toWestinghouse Electric) between 1948 and 1954, and adapted to batterychargers by W. B. Burkett and others (assigned to Christie ElectricCorp) around 1971.

An added benefit of pulsed charging is that it allows much highercurrent density in the charge pulse, which may significantly reduce thecharge time. There are practical considerations such as current carryingcapacity of the internal battery structure that must be observed, soextremely short charge cycles (less than 0.1 hour) are rarely practical,but still may be possible. Major concern of a high rate charging systemcenters around when to stop charging, since even a moderate overchargewill cause battery temperature to rise drastically, and can causeexplosion. Traditional approaches have been to stay on the safe side andterminate charging well before peak capacity has been achieved. Morecomplex control schemes have been devised (e.g. U.S. Pat. No. 4,746,852to Martin), but are largely limited to specific battery types where thecharge curve is predictable. Many of these approaches depend on furtherinstrumentation of the battery pack through addition of temperature orother sensors. In the case of the example above, identification modulesare used to select a specific control mode based upon the signaling of aspecific battery type.

It has been known for several years to vary the rate or end-point ofbattery charging as a function of 0^(th), 1^(st), 2^(nd) and 3^(rd)order sense parameters. 0th order sense parameters are those which donot vary over time. Examples include the expected maximum (reference)voltage of a particular type of battery, the maximum safe temperature ofthe battery during charging, or the maximum safe charging current. 1storder sense parameters are those which do vary over time. Examplesinclude power supply voltage (V_(ps)), battery voltage upon applicationof a given load (V_(load)), battery voltage without any load(V_(unload)), and the three corresponding currents (I^(ps)), (I_(load))and (I_(unload)). 2^(nd) order sense parameters are time derivatives ofthe 1^(st) order sense parameters, and 3^(rd) order parameters are timederivatives of the 2^(nd) order parameters. Examples include the 2^(nd)order parameter V′_(ps), (which is dV_(ps)/dt), and V″_(ps), (which isdV² _(ps)/d²t).

Known battery chargers have employed relatively simple combinations of0^(th), 1^(st), 2^(nd) and 3^(rd) order sense parameters. For example,chargers are known which modify one or more charging parameters as afunction of two different 1st order sense parameters, power supplyvoltage (V_(ps)) and temperature (T), but no second or third orderparameters. Other chargers are known which modify one or more chargingparameters as a function of one 1st order sense parameters such astemperature (T) and two different 2nd order sense parameters such asV′_(ps) and T″. As used herein, “different sense parameters” means senseparameters which are functionally independent from one another. Thus,multiple time points of the same parameter, such as two temperaturemeasurements at times T1 and T2 would constitute only one senseparameter. Similarly, corresponding voltage and current measurementssuch as V′_(ps) and I′_(ps), power supply voltage and current,respectively, would constitute only one sense parameter.

Battery Dischargers

Batteries are normally discharged continuously during operation of amotor or other load. In many cases the battery terminals are simplyconnected to the load through a variable resistor, which in the case ofa motor acts as the throttle. Such an arrangement is inherentlyinefficient because the resistor dissipates electrical power from thebattery, especially at relatively small loads.

The inherent inefficiency of resistor control has been addressed formany years by pulsing the current through an electric motor, and varyingthe duty cycle of the pulses. In most instances the pulse frequencyremains constant, and the duty cycle is varied by varying pulse width.In such circumstances, the pulse widths (durations) are directly relatedto the amount of energy received by the motor, and consequently controlthe speed of the motor. The longer the pulse width, the greater thespeed of the motor.

The switching circuitry in pulsed motor controllers often makes use ofsilicon control rectifiers (SCRs) and metal oxide semiconductor fieldeffect transistors (MOSFETs). These components, however, are notcompletely satisfactory, since operation of SCRs and MOSFETsdeteriorates in high power applications involving relatively hightemperatures. Past attempts to utilize SCRs and MOSFETs in suchapplications suffered from severe reliability problems.

A significant improvement to this technology is set forth in copendingU.S. application Ser. No. 08/437,613, (the '613 application) which isincorporated herein by reference. The '613 application describes abattery discharging circuit which translates a mechanical throttleposition into a high frequency voltage, current, or resistance levelsignal that can be converted by pulse width modulation circuitry into apulsed wave form. The pulsed wave form signal then drives an array ofpreferably MOSFET solid state switches to control the flow of currentthrough a DC electric motor. In particularly preferred circuits thesignals operate at a frequency greater than 19.4 KHz, and they drive aplurality of parallel buss-mounted MOSFET devices which share the loadof the external DC motor. Such circuits may also advantageouslyincorporate elements that raise the reliability of the overall circuitwhile still providing versatility in application, includingunder-voltage as well as over voltage protection and significant levelsof signal filtering.

Loads

In most cases the load is already designed to utilize the minimum powerrequired, if only to minimize waste heat. In such instances there may beonly minimal benefit in designing the load to cooperate with particularbattery systems, chargers and dischargers.

With respect to electric vehicles, however, the situation is somewhatdifferent in that the momentum of the vehicle can be channeled backthrough either the primary load of the main drive motor, or through anauxiliary braking generators. Many such systems, generically known asregenerative braking systems, are taught in the prior art.

A significant difficulty encountered with known regenerative brakingsystems, however, is that the brakes may provide the main battery packwith a higher energy density than can be effectively utilized withoutdamage. This problem has not been adequately solved by the prior artbecause known chargers are inadequate to safely charge known batterypacks with sufficient speed to accommodate the power developed by theregenerative braking.

Combinations

Despite the fact that numerous combinations of batteries, batterychargers, battery dischargers and loads are already known, all presentlyknown combinations are thought to be inadequate for commerciallyfeasible self-contained electric cars and other vehicles. Among otherproblems, the battery charging circuitry is generally too heavy orvoluminous to be carried on the vehicle, and manufacturers currentlycontemplate home or office charging units which can be coupled to amotor vehicle during charging, and then uncoupled during operation ofthe vehicle.

British patent application, GB 2 087 767 to Robert Bosch GmbH, doesdescribes a circuit which combines a common, on-board, pulsed powersource with both a battery and various other loads, but the non-batteryloads in that case are small loads such as a stepper motors andillumination lamps. There is clearly neither teaching nor suggestionthat a common pulsed power source can be used to drive both a batteryand a high power load such as a drive motor.

Thus, there is a strong need to integrate battery, battery charging andbattery discharging technologies, along with regenerative braking whereapplicable, to improve the overall efficiency of battery powereddevices, and especially to render electric vehicles more practical byallowing both charger and discharger to be feasibly carried on thevehicles.

SUMMARY OF THE INVENTION

The present invention is directed to battery powered devices, includingelectric vehicles, where at least one of the loads is a high power loadsuch as a drive motor, and in which both the charging and dischargingsystems share significant components such as a pulsing subsystem. Inparticularly preferred embodiments the battery and regenerative brakingsystem (where applicable) are selected to operate efficiently with thecharging and discharging systems.

Various objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of preferred embodiments of the invention, along with theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a preferred embodiment of the present invention.

DETAILED DESCRIPTION

In FIG. 1 a device such as a motor vehicle (additional details of whichare not shown) has a power supply 10, a control system 20, a directcurrent (DC) electric drive motor 50, a throttle 42 and a regenerativebraking system 90.

Batteries 12 can comprise any type of secondary (rechargeable) battery,including common lead acid, Nickel-Cadmium and so forth. Semisolid orsolid electrolyte batteries are, however, presently preferred overliquid electrolyte batteries due to safety considerations regardingspillage of electrolyte. Batteries 12 can also comprise either a singlebattery or a plurality of batteries which are electrically connected toone another. The rated voltage of power supply 10 depends largely uponthe application involved. In electric vehicles, power supply 10 mayadvantageously have a rated voltage of between 120 Volts and 156 Volts,and preferably 144 Volts. This allows the vehicle to be charged using110-117 Volt AC power from a wall socket without necessitating atransformer, and further allows the battery to be connected to the powergrid using small gauge wiring. In other applications such as hand toolsor computers, battery 12 would likely have a much lower rated voltage,such as 12 volts or less.

Control system 20 generally includes a power buss line 22, twosource/drain (s/d) buss lines 24A, 24B, two gate lines 26A and 26B, oneor more power MOSFETs 28A, 28B, and 28C, a heat sink 30, a pulsingcircuit 40, and a plurality of sensors such as a throttle sensor 42 anda braking sensor 44. During discharge of the battery 12 to operate themotor 50, one terminal 13 of battery 12 is electrically coupled to aterminal 52 of motor 50 through buss line 22, while the other terminal14 of battery 12 is coupled to the other terminal 51 of motor 50 throughs/d line 24A, power MOSFETS 28A, 28B and 28C, and s/d line 24B. Pulsingcircuit 40 provides pulses to gate line 26A under control of a logic orother control circuitry 46, which in turn operates MOSFETS 28A, 28B and28C to allow current to pass from s/d line 24A to 24B to operate themotor 50. As discussed above, the power delivered by the motor 50 isproportional to the duty cycle of the pulses provided to gate line 26A.The duty cycle can be modified by pulse width or otherwise.

Charging of the battery 12 is accomplished in a similar manner. Anexternal power supply such as an AC power source 80 and/or aregenerative braking power source 90 is electrically coupled to oneterminal 13 of the battery 12 through buss line 22, and to the otherterminal 14 of the battery 12 through the s/d line 24B, power MOSFETS28A, 28B and 28C, and s/d line 24A. In this case, however, pulsingcircuit 40 provides pulses to gate line 26B, which in turn operatesMOSFETS 28A, 28B and 28C to allow current to pass from s/d line 24A to24B to operate the motor 50. As discussed above, the power delivered bythe motor 50 is proportional to the duty cycle of the pulses provided togate line 26A.

The external power supply 80 will, of course, need to be interruptablycoupled to the on-board circuits, and this is shown as connections 81,82. By matching the operation of the pulsing circuit 40 to properlyutilize the inherent frequency of the external power supply, noadditional on-board or off-board rectifier is required. Thus, forexample, if the pulsing circuit is operating at 19.8 KHz, and theexternal power supply 80 is providing power at 60 Hz, 330 pulses of thepulsing circuit 40 will correspond to each cycle of current provided bythe external power supply 80. Similar matching can take place withrespect to the power supplied by the regenerative braking 90, andpreferably in such manner that the circuitry automatically compensatesfor varying frequency of the power produced by the regenerativebreaking.

The DC electric drive motor 50 is contemplated to move the motorcontaining device substantially continuously with respect to an externalobject Thus, in an electric vehicle motor 50 would provide the motiveforce to propel the vehicle forward or backward, while in an electrichand tool such as a portable drill or saw, motor 50 would provide themotive force to turn a drill bit or move a saw blade. Under thisdefinition the term “DC electric drive motor” would not include electricmotors which are intended to operate only internally, or intermittently,such as a stepper motor used to position a head in a compact diskette(CD) player. Except for those limitations, motor 50 should beinterpreted broadly to include motors of virtually any size and powerrating, winding configuration and so forth.

It is contemplated that the pulsing circuit 40 will operate at a highfrequency—preferably at least 19.4 KHz, and more preferably at least 20KHz. The wave forms are presently contemplated to be approximatelysquare or triangular, although all other wave forms are contemplated aswell.

Thus, while specific embodiments and applications of this invention havebeen shown and described, it would be apparent to those skilled in theart that many more modifications are possible without departing from theinventive concepts herein. The invention, therefore, is not to berestricted except in the spirit of the appended claims.

What is claimed is:
 1. A battery powered device comprising: a battery; abattery control system having a main charging subsystem and a maindischarging subsystem, wherein the charging and discharging subsystemsshare at least one of the following: (a) a duty cycle modulator; (b) acurrent carrying bus bar; and (3) a transistor heat sink; and a DCelectric drive motor.
 2. The device of claim 1 wherein the charging anddischarging subsystem share at least two of the following: (a) a dutycycle modulator; (b) a current carrying bus bar; and (3) a transistorheat sink.
 3. The device of claim 1 wherein the duty cycle modulatorproduces pulses having varied pulse widths.
 4. The device of claim 1further comprising a battery pack having a rated voltage of between 120V and 156 V.
 5. The device of claim 1 wherein the battery contains apolymer electrolyte.
 6. A battery powered device comprising: a battery;a battery control system having a main charging subsystem and a maindischarging subsystem, wherein the charging and discharging subsystemsshare at least one of the following: (a) a duty cycle modulator; (b) acurrent carrying bus bar; and (3) a transistor heat sink; and a DCelectric drive motor; wherein the duty cycle modulator produces pulsesat a frequency of at least 19,600 Hz.
 7. The device of claim 6 whereinthe duty cycle modulator produces pulses at a frequency of at least20,000 Hz.
 8. An electric vehicle comprising: a battery; a batterycontrol system having a pulsed on-board main charging subsystem and apulsed on-board main discharging subsystem, and a DC electric drivemotor.
 9. An electric vehicle comprising: a battery; a battery controlsystem having a pulsed on-board main charging subsystem and a pulsedon-board main discharging subsystem, and a DC electric drive motor;wherein the duty cycle modulator produces pulses at a frequency of atleast 19,600 Hz., with varied pulse widths.
 10. The device of claim 9further comprising a regenerative braking system which generateselectrical power upon braking, wherein at least a portion of theelectrical power generated thereby is used to charge the battery. 11.The device of claim 10 further comprising a battery pack having a ratedvoltage of between 120 V and 156 V.
 12. A battery powered devicecomprising: a battery; a battery control system having a duty cyclemodulator which produces pulses at a frequency of at least 19,600 Hz.;and a DC electric drive motor.
 13. The device of claim 12 wherein thebattery control system comprises a main charging subsystem and a maindischarging subsystem, and the duty cycle modulator is shared by boththe charging subsystem and the discharging subsystem.